Support for pause/resume of game rendering loop (#476)

* added pause/resume

* don't override displaymode in game engine

* avoid setting light sensing display mode

libs/core/led.cpp

@@ -96,6 +96,14 @@ namespace led {
         uBit.display.setDisplayMode((DisplayMode)mode);
     }
 
+    /**
+    * Gets the current display mode
+    */
+    //% weight=1 parts="ledmatrix" advanced=true
+    DisplayMode_ displayMode() {
+        return (DisplayMode_)uBit.display.getDisplayMode();
+    }
+
     /**
     * Turns on or off the display
     */